Sunshine and Vitamin D

Author: Winston Craig, MPH, PhD, RD.

Ultraviolet radiation from the sun triggers vitamin D synthesis in the exposed skin.

The mere mention of the word osteoporosis brings to mind brittle bones, painful compression fractures of the spine, permanent lower back pain, hip fractures, and permanent disability or death. This year over a million Americans will suffer a bone fracture due to osteoporosis. Do only women lose bone mass? No. Men lose about 1% of their bone mass per year after age 55-60. What causes bone loss? We generally consider insufficient dietary calcium, too much salt and protein causing increased calcium losses, hormonal changes, and too little regular weight-bearing exercise to be the culprits. Often overlooked is vitamin D deficiency. In Boston, one-third of adults over the age of 50 who were admitted to a hospital for any reason were found to be borderline to overtly vitamin D deficient. Vitamin D is essential for adequate calcium absorption and bone health.

What are the Symptoms of Vitamin D Deficiency?

None really, except that calcium absorption is restricted. To maintain blood calcium levels, bones will donate calcium. Thus the result of vitamin D deficiency is acceleration of bone loss and increased risk of bone fracture at an earlier age.

From Where Do We Get Vitamin D, Other Than Fish Oils?

There is a limited number of foods that are fortified with vitamin D2 (ergocalciferol), including milk (but not yogurt or cheese), margarine, fortified soy and rice beverages, and some ready-to-eat cereals. In addition, puddings and other desserts containing D-fortified milk will contain vitamin D. One serving of each of these foods provides only 1-3 micrograms of vitamin D while the RDA is 5-10 micrograms, depending upon one’s age.

Regular exposure to sunshine, in addition to helping fight depression, also improves bone density. This is because vitamin D is made by the action of sunlight on the skin. How much sunlight does one really need for D synthesis? Well, it depends upon the time of day, season of the year, where you live, your age, and how much pigmentation occurs in your skin. Sunlight is not very intense before 8 am or after 5 pm. Many people seek protection from the sun by using sunscreens which block out the UV-B rays that make vitamin D. A sunscreen with an SPF of 8 prevents 95% of vitamin D production in the skin. For SPF 30 there is 99-100% blockage.

People who live at high latitudes can’t make vitamin D during winter months because of the low angle of the sun, so that blood levels of vitamin D are usually lower in wintertime. Women in Bangor, Maine lost about 3% of their bone mass during winter due to decreased vitamin D blood levels. Part of the loss was recovered the following summer. People living in Boston and Chicago and further north can’t make vitamin D from November to February while people in Columbus, Ohio and Denver cannot make vitamin D during January and February. People in Southern California, Texas or Florida receive sunlight all year around that is intense enough for adequate vitamin D synthesis.

Older people may not get enough vitamin D, since going outdoors may be restricted due to fear of wrinkles and skin cancer. Taking a walk in the sunlight is really a great idea. It increases muscle tone, maintains bone strength, and provides vitamin D. Sun exposure to the hands and face for about 10-15 minutes a day, during the middle of the day, about 3 times per week is usually sufficient for adequate vitamin D synthesis. In addition to improving bone density, vitamin D has also been found to inhibit the growth of cancer cells. A recent study showed that it provided protection against breast cancer.

Can One Get Too Much Vitamin D?

In excess, vitamin D is toxic. In fact, it is the most toxic of all vitamins. It causes calcification of soft tissues, and may cause calcified kidneys and kidney failure. Too much vitamin D may elevate blood calcium to high levels and produce fatigue and mental confusion.

So, when the first warm days of spring arrive we must resist the urge to make a lemming-like dash to the beach for a suntan. Health authorities warn us that if we don’t like freckles, sunspots, rough skin or wrinkles then we had better not overdo our sun worship! But moderate amounts of regular sunshine will provide us necessary vitamin D.